The present invention relates to an apparatus for quantizing a classified vector of a video signal, and more particularly, to an apparatus for efficiently quantizing a classified vector of an image signal having a low transmission rate.
The use of a vector quantizer to enhance encoding efficiency when an image signal is encoded at a low encoding ratio is presently being studied. An existing vector quantizer uses a correlation between vectors to obtain an encoding gain which is greater than that obtained with a scalar quantizer. However, when such a vector quantizer is used, distortion occurs at the edge portion of the image.
A classified vector quantizer is used to obviate such a defect. To accomplish the substantial elimination of distortion, image data of a spatial domain is converted into transform coefficients of a frequency domain or a transform domain through a discrete cosine transform operation which is performed in units of 8.times.8 blocks. Each block partitioning an image is classified into various classes according to edge components of the image. The classified vector quantizer quantizes an image signal using vectors partitioning 8.times.8 blocks of a frequency domain and a code book designed to be appropriate for various classes of blocks.
The aforementioned existing classified vector quantizer quantizes classified vectors of the transform coefficients obtained by using a discrete cosine transformation. As a result, an image signal having a low transmission rate brings about blocking effects in which a boundary portion between the blocks is displayed. Also, a product code is used to reduce the amount of data required for representation of vectors partitioning the 8.times.8 blocks, which requires a complicated structure of the classified vector quantizer.